Product description

Ring USM (Ultrasonic motor) uses ultrasonic frequency vibrations to drive responsive, near-silent high speed auto focus. Good holding torque stops the focusing lens group with precision without overshoot. Full time manual focus override is available without having to switch out of AF. Two UD (ultra-low dispersion) glass lens element correct chromatic aberration to achieve high resolution and contrast, without color fringing on subject outlines. Two AL aspherical lens elements suppress aberrations for high image quality at all focal lengths. Equipped with a fixed, petal-type hood and a gelatin filter holder at the rear. Only lead free glass is used in the lens construction.

While its large diameter, high-precision aspherical and UD elements, optimized lens element positioning, and flare and ghost-reducing lens coating ensure that this lens delivers the top optical performance in its professional class, Canon has added other features photographers have been asking for--improved dust and water resistance incorporated around the mount, switch panel and focusing ring, and a round aperture that creates a nice background blur and makes it easier to recognize an out-of-focus scene in less than brightly lit conditions.